TORSION OF THE CRUSTACEAN LIMB. 



135 



decided approach to the brachyurans, or true crabs is seen in the 

 short tail, the broad carapace armed with marginal spines, as 

 well as in the slender antennas and other appendages so far as 

 they are known. Very significant also is the fact that as in the 

 modern crab the claws open obliquely outward. 



In the homarine Hoploparia> found in the Cretaceous and 

 early Tertiary periods, the form of the large chelipeds renders it 

 highly probable that a torsion of this limb had already taken 

 place. At all events this phenomenon has a very ancient history, 

 and is probably older than autotomy which precedes the regen- 



Fig. 4 



D 



FIG. 4. First larva of lobster from above, showing the outwardly opening claw 

 of the first pair of chelipeds. D, dactyle. 



FIG. 5- Fourth larva or lobsterling stage of the lobster, showing the big claw- 

 feet, in which torsion is complete, opening inward, toward the middle line of the 

 body. D, dactyle. 



eration of certain limbs, and which in the most perfect cases is 

 dependent upon a fusion of the second and third joints. In the 

 lobster this fusion does not occur until after the fifth molt. 



II. 



When we attempt to answer the question How could a tor- 

 sion of the crustacean limb be effected ? the results are not very 

 reassuring upon either Lamarckian or Darwinian principles. The 



